Abstract
The molecular mechanisms that underlie sex determination and differentiation are conserved and diversified. In fish species, temperature-dependent sex determination and differentiation seem to be ubiquitous and molecular players involved in these mechanisms may be conserved. Although how the ambient temperature transduces signals to the undifferentiated gonads remains to be elucidated, the genes downstream in the sex differentiation pathway are shared between sex-determining mechanisms. In this paper, we review recent advances on the molecular players that participate in the sex determination and differentiation in fish species, by putting emphasis on temperature-dependent sex determination and differentiation, which include temperature-dependent sex determination and genetic sex determination plus temperature effects. Application of temperature-dependent sex differentiation in farmed fish and the consequences of temperature-induced sex reversal are discussed.
Highlights
Sex-determining mechanisms are responsible for a population’s sex ratio, which is the ratio of males to females in the population, a key demographic parameter for its viability and stability
genetic sex determination (GSD) occurs when primary sex is determined by the genotype at conception and is thereafter independent of environmental conditions
First we review the genes that are known to play a role in GSD, and the genes that are expressed downstream in the sex determination cascade and involved in temperature-dependent sex determination (TSD) and GSD + Genetic sex determination plus temperature effects (TE) and in the putative mechanisms that underlie the effect of temperature on sex differentiation
Summary
Sex-determining mechanisms are responsible for a population’s sex ratio, which is the ratio of males to females in the population, a key demographic parameter for its viability and stability. In spite of the diverse and seemingly paradoxical expression patterns of dmrt found among different types of sex determination systems involved in temperature-dependent sex reversal, it is clear that dmrt plays an essential role in testis differentiation and in the temperature signal transduction pathway to the gonad at least in fish species with TSD, and that the up-regulation of dmrt expression is correlated with the temperature-induced male phenotype. Kitano et al [133] have studied the Japanese flounder (Paralichthys olivaceus), in which sex is genetically determined with strong temperature effects since high temperatures induced an all-male population from an all-female population They reported that, in this species, the expression of cyp19a1a mRNA was the same between males and females during the sex-undifferentiated period up to 50 DPH but that 10 days later when gonads start to differentiate, a specific expression was detected in the females. Overexpression and knockdown techniques allow us to investigate whether these molecular players are necessary and / or sufficient to explain the fate of sexual direction as already shown for the genes amhr in fugu [50], amhy in Patagonian pejerrey [48], sdY in rainbow trout [51], and dmy in medaka [31,32] and the genes in other vertebrates [213,214,215,216,217,218,219,220] (Figure 2)
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